There is great concern regarding the potential developmental and reproductive effects resulting from environmental exposure to endocrine disrupting compounds (EDCs). Recent population trends showing shifts in the age of puberty onset and progression have contributed to this concern, as has evidence for interrelationships between EDC exposures, overweight and obesity, and eadier onset of puberty. Early and late puberty onset are associated with social and psychological challenges and may indicate risk of current or future endocrine-related disorders. EDCs, such as phthalates and BPA, have been hypothesized to be associated with earlier puberty, while animal and human studies suggest exposure to lead and cadmium may be associated with delayed growth and puberty onset via endocrine-mediated pathways. There are a lack of longitudinal studies that have considered exposure to these agents, individually and as mixtures, and at multiple sensitive stages of development, in relation to physical growth and sexual maturation. The proposed study will address these gaps by expanding on pilot work ofthe University of Michigan (UM) Formative P20 Children's Center to undertake a more robust (N = 400) prospective assessment ofthe relationship between exposure to a select mixture of EDCs (phthalates, BPA, lead, and cadmium) and the tempo of physical growth and timing of sexual maturation in a long-standing longitudinal cohort study in Mexico. Existing data on life stage lead exposure and anthropometry (height, weight, BMI) 6-month intervals between birth and 5 years of age will be utilized, along with newly collected data. In the proposed study, children in the ongoing cohort will be re-recruited for two clinic visits (18 months apart) between the ages of 8 and 15 where Tanner stages (along with testicular volume among boys), anthropometry, and skjn fold thickness will be assessed by a clinician, a blood sample will be collected for analysis of lead and reproductive and thyroid hormones, and a urine sample will be collected for analysis of phthalates, BPA and cadmium. These same exposure measures will additionally be analyzed from samples collected at all 3 trimesters of pregnancy when the children were in utero. Four years of repeated self-reported Tanner stage